Place the dry pasta, diced tomatoes (with their liquid), chicken broth, minced garlic, sun-dried tomatoes, Italian seasoning, red pepper flakes, salt, and pepper directly into the basin of a 6-quart slow cooker.

Stir all ingredients together thoroughly until the pasta is submerged as much as possible in the liquid.

Cover the slow cooker and cook on LOW for 3 hours or on HIGH for 1.5 to 2 hours. Check occasionally to ensure the pasta is tender but not overly soft, stirring halfway through.

Once the pasta is cooked, stir in the cubed cream cheese until it has almost completely melted into the sauce. Then, mix in the heavy cream and grated Parmesan cheese until the sauce is smooth and creamy.

Add the fresh spinach to the pot. Stir gently until the spinach wilts completely into the sauce, which should take about 5-10 minutes.

Taste and adjust seasoning if necessary (add more salt or pepper). Serve immediately, garnished with extra Parmesan cheese if desired.